The general field with which this invention is concerned is in the area of treating the surfaces of articles being manufactured, particularly by casting, wherein a particulate material, known as the blasting medium, is forcefully hurled against the surfaces of workpieces to clean the surfaces or remove unwanted portions thereof. The general method of blasting in this fashion, and certain devices for accomplishing various kinds of blasting, are known and will not be described herein. The blasting medium itself is chosen to be consistent with the nature of the task to be performed and with the characteristics of the material from which the workpiece is made. The blasting medium can consist of relatively small abrasive particles or can be substantially spherical shot, but the specific characteristics of the blasting medium are of little significance to the invention disclosed herein.
Special problems are presented in treating the surfaces of workpieces which are particularly large in volume or surface area, and machines designed for handling numbers of small workpieces are simply not usable to handle the larger ones. A machine for dealing with relatively large workpieces is shown in German Offenlegungsschrift No. 25 25 761 wherein a blasting chamber contains a bracket which is disposed on a movable column, the bracket being vertically shiftable thereon. The bracket is designed to accomplish one symmetrical bending movement and a single blasting wheel for propelling the blasting medium, movable in two planes, is mounted on the bracket. With that apparatus it is not possible to simultaneously blast several surfaces, such as, for example, the peripheral and front surfaces, of a workpiece.
The large number of directions of movement required in that prior art apparatus imply a corresponding number of adjusting drive mechanisms which are exposed to the jets of blasting material, and also an expensive control and a flexible feed for the blasting medium to the blasting wheel, all of which increase the likelihood of difficulty in maintaining and operating the apparatus.
In addition, significant time is consumed in treating the surfaces of a large workpiece with that apparatus.